Methods and Cases for Calculating Patent Infringement Damages

In patent infringement litigation, securing actual relief, i.e., a reasonable and sufficient amount of damages, is as important as obtaining a favorable judgment. Article 128 of the Korean Patent Act provides various legal frameworks for calculating damages, and its importance and complexity have further increased, especially with the introduction and strengthening of punitive damages through the 2019 and 2024 amendments.

This column aims to provide an in-depth analysis for legal professionals on the legal basis, practical issues, case law trends, and strategic utilization of each damage calculation method stipulated in Article 128 of the Patent Act, with a particular focus on the application standards and implications of the strengthened punitive damages system.

Basis of Lost Profits for Patent Holder: Calculation of Lost Profits (Articles 128(2), 128(3))

1. Basic Legal Principles and Calculation Formula
Article 128(2) of the Patent Act presents the first method for estimating damages as lost profits, which are the profits the patent holder could have earned had the infringement not occurred. The formula is: “Infringing Sales Volume × Profit Per Unit for Patent Holder.”

2. Analysis of Key Variables and Practical Issues

Infringing Sales Volume (Qinfringement): In principle, the total volume sold by the infringer is the standard, but it is limited by production capacity and market factors discussed later. While the infringer bears the burden of proving sales volume, it is generally secured through discovery procedures such as orders for submission of documents (Patent Act Article 132).
Profit Per Unit for Patent Holder (πPatent Holder): Case law consistently applies the concept of 'Marginal Profit' or 'Contribution Margin'. This means that only variable costs directly linked to the production and sale of the product (material costs, direct labor costs, sales commissions, etc.) are deducted from revenue, while fixed costs (facility depreciation, general administrative expenses, fixed labor costs, etc.) are excluded. This is based on the logic that deducting costs not incurred additionally due to infringement would be unfair.
- Practical Issues: Ambiguous items distinguishing variable and fixed costs (e.g., semi-variable costs) and the issue of allocating common costs when producing multiple products can arise, often requiring appraisal or analysis by accounting experts.

3. Limiting Factors in Damage Calculation

Limitation by Production Capacity (Proviso to Article 128(2)): The amount of damages is capped by the patent holder's remaining production capacity, calculated as the difference between the quantity that can be produced and the quantity actually sold (Qproducible - Qactual sales).
- Practical Issues: Disputes may arise regarding the standard for 'production capacity' (theoretical maximum vs. realistic operating rate), whether external production is included, and whether plans for increasing production capacity are recognized. The patent holder must prove specific production capacity through production facilities, personnel, and past performance.
Deduction of Market Factors Other Than Infringement (Article 128(3)): Portions of damages that would not have been sold by the patent holder due to reasons other than the infringing act (e.g., existence of competing products, lack of market demand, patent holder's insufficient marketing capabilities) must be deducted from the damages.
- Practical Issues: The deduction ratio is determined by comprehensively considering the competitive landscape, the substitutability of each product, price competitiveness, brand recognition, etc. (utilizing market share analysis, etc.). The infringer can claim deductions by actively proving the existence and market impact of non-infringing alternatives. This is directly linked to the issue of causation between the damages and the infringing act. The four elements from US case law, Panduit (existence of demand, absence of non-infringing alternatives, production/marketing capability, magnitude of profit), may be referenced.

4. Comprehensive Calculation Formula and Strategic Considerations
The final lost profits damages can be formalized as follows:
Damages (Lost Profits) = Min{Qinfringement, (Qproducible - Qactual sales)} × πPatent Holder × (1 - Market Factor Deduction Rate)
The patent holder's strategy is to maximize damages by proving a high marginal profit rate, sufficient production capacity, and strong market dominance (low deduction rate).

Basis of Infringer's Profits: Estimation of Profits (Article 128(4))

1. Basic Legal Principles and Effect of Estimation
Article 128(4) of the Patent Act 'presumes' the profits earned by the infringer from the infringing act as the patent holder's damages. This provision is intended to reduce the patent holder's burden of proving damages.

2. Analysis of Key Variables and Practical Issues

Infringer's Profits: This is the amount obtained by deducting costs directly related to the production and sale of infringing goods from the total sales revenue of the infringing goods. Case law tends to interpret the deductible costs here as primarily variable costs (see Supreme Court Decision 2006da17609, etc.), although there may be some room for broader recognition than the patent holder's costs when calculating lost profits.
- Practical Issues: When the infringer produces multiple products, the key issues are accurately separating sales and cost data for the infringing products and establishing reasonable allocation standards for common expenses (e.g., by sales ratio, production volume ratio). The amended Patent Act Article 132 (Order for Submission of Data) in 2019 provides substantial assistance in securing the infringer's accounting data. The fact that failure to comply can lead to the patent holder's claims being presumed true (Article 132(6)) is a powerful leverage.
Rebuttal of Presumption (Proviso to Article 128(4)): The infringer can claim a reduction based on their contribution (Apportionment) by proving that a portion of their profits is attributable to factors unrelated to the patented technology (e.g., their own technological capabilities, design, brand value, marketing efforts).
- Practical Issues: Proving the degree of contribution is a very challenging task. The infringer must persuasively present specific evidence (e.g., details of their own R&D investment, marketing expense records, brand valuation data, analysis of the technical/commercial importance of non-infringing elements) to demonstrate that the contribution of the patented technology is limited. The court will determine a reasonable contribution rate by considering the arguments of both parties.

3. Strategic Considerations
The infringer's profits method is particularly useful when the patent holder's production capacity is low, their marginal profit is small, or when the infringer's profit margin is very high. The patent holder needs to actively utilize orders for the submission of data to understand the infringer's sales and cost structure and to effectively counter the infringer's claims of contribution.

Basis of Hypothetical License Fee: Calculation of Reasonable Royalty (Articles 128(5), 128(6))

1. Basic Legal Principles and Purpose of Amendment
If proving lost profits or infringer's profits is difficult, or if the amounts calculated by these methods are minimal, the patent holder can claim as damages the amount that could have been 'reasonably received' for the use of the patent (Reasonable Royalty) (Article 128(5)). The change from 'customarily received amount' to 'reasonably received amount' before the 2019 amendment was intended to allow for a more flexible and appropriate royalty calculation through a hypothetical license negotiation, even when there is no objectively established royalty rate. This is similar to the approach of determining specific rates on a case-by-case basis, referencing the Georgia-Pacific factors from US case law.

2. Calculation Formula and Factors Determining Royalty Rate
Damages (Reasonable Royalty) = Revenue of Infringing Products (or Sales Volume) × Reasonable Royalty Rate (or Per-Unit Royalty)
The factors considered in determining the reasonable royalty rate/fee are as follows:

Established royalty, if any, serves as a strong benchmark.
Industrial practices in the relevant technology field and licensing examples of similar technologies.
Importance, innovativeness, commercial value, and market contribution of the patented technology.
Existence of non-infringing alternative technologies and the technical/cost gap.
Patent term and the strength of the scope of rights.
Whether the license agreement is exclusive.
Possibility of additional profits from sales related to infringing products (Convoyed Sales).
Business situations and expected profits of the parties at the time of hypothetical negotiation.

3. Practical Issues and Relationship with Article 128(6)

Practical Issues: Calculating a 'reasonable' royalty rate is essentially a valuation problem. Appraisals by technology valuation experts, analysis of industry licensing databases, and similar litigation cases are utilized. The patent holder will argue for a high royalty rate by highlighting the technology's superiority and market contribution, while the infringer will argue for a lower rate by citing the existence of alternative technologies, low contribution, etc.
Meaning of Article 128(6): This provision clarifies that if the reasonable royalty amount is less than the actual damages incurred (e.g., lost profits), the difference can be claimed additionally. This confirms the principle that a reasonable royalty serves as a 'floor' for damages, and the patent holder can recover damages exceeding this amount if provable.

4. Strategic Considerations
A reasonable royalty serves as a last resort when proving other methods is difficult and as a means to supplement damages by combining it with other methods. The patent holder should prepare thorough valuation grounds to pursue a strategy of maximizing the 'reasonable' level.

Combined Application of Multiple Methods and Other Damages (Article 128(7), etc.)

Article 128(7) of the Patent Act grants the court discretion to recognize reasonable damages by considering the entirety of the arguments and the results of evidence examination during damage calculation, thereby supporting the possibility of applying multiple methods in combination.

Typical Combination: Lost Profits + Reasonable Royalty: Case law has established a method of calculating lost profits (Article 2) for infringing sales within the patent holder's production capacity and reasonable royalties (Article 5) for sales exceeding production capacity, and then summing them up (Supreme Court Decision 2006da17609, etc.). This aligns with the fundamental principle of civil damages, which aims for full compensation.
Price Erosion Damages: The decrease in profits caused by the patent holder's unavoidable price reduction due to the infringer's low-price sales can theoretically be included in the scope of damages. However, Korean case law tends to view this as special damages, distinct from ordinary damages, requiring additional proof of the infringer's foreseeability (knew or could have known), making it difficult to prove. Sophisticated economic analysis is necessary for causation and damage calculation.
Other Considerations: When calculating damages, the court may adjust the final amount considering all circumstances based on the principle of equity.

Punitive Damages for Intentional Infringement (Articles 128(8), 128(9))

1. Overview of the System and 5x Increase
The punitive damages system, introduced in 2019, allows the court to increase damages (basic damages) recognized under Articles 2 through 7 by up to five times if the infringement was 'willful' (Article 128(8), amended Feb 2024, effective Aug 2024). The purpose is to prevent and deter infringing acts beyond mere compensation for damages.

2. Criteria for Determining 'Intentionality'
'Intentionality' is interpreted to include not only recognizing the existence of a patent but also proceeding with infringement while knowing it is infringing, or recklessly continuing infringing acts despite being fully aware of the possibility of infringement.

Practical Judgment Factors: Evidence such as the patent holder's receipt of a warning letter and their response, efforts to avoid competitor patents (e.g., Freedom-to-Operate analysis), internal documents (emails, meeting minutes, etc.), and the acquisition and content of expert opinions from patent attorneys/lawyers are important evidence for determining intent. The infringer may attempt to deny intent by arguing that there were valid non-infringement or invalidity arguments, or that they relied on expert opinions of non-infringement.

3. Criteria for Determining Multiplier Increase (8 Factors in Article 128(9))
The court determines whether to increase damages and the multiplier by 'considering' the following 8 factors. This provides guidelines for discretionary judgment.

Infringer's Superior Position: Judgment of unfairness, such as abuse of bargaining power.
Degree of Intent or Awareness of Damage Occurrence: The degree of malice is key.
Magnitude of Damages: Consideration of the actual extent of harm beyond the basic damages.
Infringer's Economic Benefit: Scale of unjust enrichment.
Duration and Frequency of Infringement: Persistence and repetition of infringement.
Criminal Penalties such as Fines: History of related criminal sanctions.
Infringer's Financial Status: Consideration of ability to pay and deterrent effect.
Remedial Efforts by Infringer: Post-infringement attitude (attempts at settlement, voluntary correction, etc.).

4. Practical Implications and Strategies

Patent Holder: Clearly assert intent from the time of filing the lawsuit and actively collect and submit relevant evidence (e.g., records of warning letters sent, infringer's internal documents, evidence of failed design-around efforts). Emphasize the necessity of applying a high multiplier by favorably constructing the eight factors.
Infringer: Denying intent is the top defense strategy. Actively argue the reasonableness of non-infringement/invalidity claims, reliance on expert opinions, and post-warning correction efforts. If intent is likely to be recognized, focus on favorable circumstances among the eight factors (e.g., low profits, remedial efforts) to seek a reduction in the multiplier.
Impact of 5x Increase: The expansion of the upper limit for increased damages has significantly raised the risk of patent infringement litigation. This further emphasizes the importance of prior patent analysis and design-around efforts for companies with potential infringement risks and may incentivize early settlement upon dispute. It is expected that specific standards and requirements for the actual application of 5x damages will be established through the accumulation of case law.

Conclusion

Calculating damages in patent infringement litigation requires a precise understanding of the legal requirements, burden of proof, and practical issues of each method, selecting and combining the most suitable methods for the specific facts of the case, and developing a multifaceted strategy that considers the enhanced punitive damages. In particular, disputes over proving intent and determining the multiplier for punitive damages are expected to become more intense.